Field of the Invention
The invention relates to a light source and, more particularly, to an LED light source, with at least one LED, a basic body formed with a recess wherein the LED is arranged, a filling of transparent material which embeds the LED and wherein a converter substance for the at least partial wavelength conversion of the light emitted by the LED is contained, and a lens in contact with the material filling.
LEDs (light-emitting diodes) based on GaN, with which blue or ultraviolet light can be generated, have recently been developed. With the aid of these LEDs, light sources can be produced on the basis of wavelength conversion. A concept, which has already been realized provides that part of the blue light emitted from the LED is converted into yellow light by a suitable converter material, so that white light is generated as a consequence of the resultant color mixing of the original blue light with the converted yellow light. In a second concept, it is proposed to convert ultraviolet light of a suitable LED into the visible spectral range.
The converter material, in the case of both concepts, may either be contained in the semiconductor material of the LED or in an embedding material of resin or the like surrounding the LED.
To increase the radiation intensity of the component in the emission direction, the LED components may be provided with an optical lens, by which the light is focused and emitted in a directed manner.
An example of a form of construction of this type is represented in FIG. 1. There, a form of LED construction is illustrated that is described, for example, in the article xe2x80x9cSIEMENS SMT-TOPLED fxc3xcr die Oberflxc3xa4chenmontagexe2x80x9d [SIEMENS SMT-TOPLED for surface mounting] by F. Mxc3x6llmer and G. Waitl in the journal Siemens Components 29 (1991), issue 4, page 147 in connection with FIG. 1. That form of LED is extremely compact and, if appropriate, allows the arrangement of a large number of LEDs of this type in a linear array or a matrix array.
In the case of a SMT-TOPLED of the configuration shown in FIG. 1, an LED 2 is mounted with one of its electrical contact areas on a leadframe 5, which is connected to one pole of a voltage source, while an opposite leadframe 5, connected to the other pole of the voltage source, is connected by a bonding wire 6 to the other electrical contact area of the LED 2. The two leadframes 5 are encapsulated in a high-temperature-resistant thermoplastic. In this way, a basic body 1, wherein there is a recess 1A into which the LED 2 protrudes from the inside is formed by injection molding. The thermoplastic preferably has a high diffuse reflectance of approximately 90%, so that the light emitted by the LED 2 can be additionally reflected at the sloping side walls of the recess 1A in the direction of the outlet opening. The recess 1A is filled with a transparent resin material 3, such as an epoxy resin, which contains a converter material, for example a suitable dye. The resin material and the thermoplastic are carefully matched with each other, in order that even peak thermal loads do not lead to mechanical problems.
During operation, blue or ultraviolet light is emitted by the LED 2, which may be produced for example on the basis of GaN or on the basis of II-VI compounds. On its path from the LED 2 to the lens 4, the relatively short-wave emitted light radiation is partially converted into longer-wave light radiation in the resin filling 3 containing the converter material. In particular, if a blue LED is used, such a converter material by which the blue light radiation is converted at least partially into yellow light radiation can be used. One problem of this type of construction, however, is that the light rays are subject to different path lengths in the resin filling 3 filled with the converter material from the LED 2 to the lens 4. These have the result that the yellow fraction in the light radiation predominates in the outer region of the component, whereas by contrast, the blue fraction in the light radiation predominates in the center. This effect consequently leads to a color locus of the emitted light radiation varying with the direction of emission or direction of viewing.
U.S. Pat. No. 3,875,456 discloses semiconductor light sources which have two semiconductor elements arranged in a housing or reflector. The semiconductor elements are embedded in a scattering layer, downstream of which there is a covering formed similar to a lens. The scattering layer and the covering may be formed by resin layers applied one on top of the other and contain phosphorescent materials.
U.S. Pat. No. 5,847,507 describes a light-emitting diode wherein the semiconductor element is enveloped by a covering in lens form, for example of epoxy resin, which contains fluorescent materials.
European patent publication EP 0 230 336 shows a component which has a substrate on which an annular spacer and an optoelectronic element are fastened. The optoelectronic element is arranged inside the annular opening. The annular opening is filled with a transparent compound and is closed off by a spherical lens, which is mounted on the annular spacer, lying opposite the substrate, and is in contact with the transparent compound.
It is accordingly an object of the invention to provide an LED light source, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and wherein the path length of the radiation through the converter material is essentially equal and the light radiation can be emitted in a focused form. In addition, a method of producing a light source of this type is to be specified.
With the foregoing and other objects in view there is provided, in accordance with the invention, an LED light source, comprising:
a basic body formed with recess;
an LED disposed in the recess;
a filling of a transparent material embedding the LED and a converter substance in the transparent material for at least partially converting a wavelength of light emitted by the LED;
a lens in contact with the filling, the lens being prefabricated and having a definitively preformed concave underside and being placed on the material filling prior to a final curing of the material filling, whereby an upper side of the material filling enters into a form fit with the concave underside of the lens and has a convex surface formed by the underside of the lens.
In accordance with an added feature of the invention, a volume of the filling is less than a free volume of the recess with the LED disposed therein.
In accordance with an additional feature of the invention, the convex surface of the filling and the underside of the lens are formed to have a substantially constant distance from the LED.
In other words, the filling has a convex upper surface defined by substantially equidistant points from the LED, i.e., it is approximately spherical with the LED forming the center of the sphere.
In accordance with another feature of the invention, the LED has an active radiating area and the convex surface of the filling and the underside of the lens are formed at a substantially constant distance from a geometrical center point of the active radiating area of the LED.
In accordance with a further feature of the invention, the LED is a blue light-emitting LED based on GaN and the converter substance converts light radiation in the blue spectral range into light radiation in the yellow spectral range. In an alternative embodiment, the LED is a UV-emitting LED and the converter substance converts UV light into a visible spectral range.
In accordance with again an added feature of the invention, a distance of the convex surface from the LED is set such that a degree of conversion along an optical path length of the light radiation is substantially 50%.
In accordance with again an additional feature of the invention, the LED has an active radiating area and a distance of the convex surface from a geometrical center point of the active radiating area is set such that a degree of conversion along an optical path length of the light radiation is substantially 50%.
In accordance with again another feature of the invention, the light source is a surface-mounted component.
In accordance with again a further feature of the invention, the filling contains a resin material, in particular an epoxy resin. In a preferred embodiment, also, the basic body contains a thermoplastic material.
In accordance with yet an added feature of the invention, there is provided:
a first leadframe carrying the LED at a first electrical contact area thereof;
a second leadframe connected to a second electrical contact area of the LED by a bond wire; and
wherein the basic body is produced by injection molding around the leadframes.
In accordance with yet an additional feature of the invention, the recess is defined by sloping and reflective side walls.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing an LED light source, which comprises the following steps:
forming a recess with a planar bottom face in a basic body;
mounting an LED on the bottom face;
filling the recess with a defined amount of a transparent material, such as a resin material, containing converter material;
providing a lens with a concave underside;
inserting the lens with the concave underside into the still liquid transparent material; and
curing the transparent material.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in LED light source with lens and a method of producing the light source, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.